Hey guys, finally was able to get my LSA swapped 96 Impala SS tuned by a competent tuner. The car drove amazing for a few days, then out of nowhere I began smelling a lot of fuel and it began flashing codes for bank 1 and 2 lean. The car still ran good, but had pretty rough start up/warm up and a little bit of an erratic idle.

I assumed the tune may have been scaled a little bit off and was "learning its way out" but when resetting LTFT, the problem arises immediately. Wouldn't make sense it was the tune if it were able to run flawlessly for several days and now won't run for 10 minutes without flashing a code after resetting LTFT

Checked for exhaust leaks, had my friend pressurize the exhaust from he back with shop air and didn't feel anything

Checked that no vacuum hoses blew off or anything, haven't seen anything but i'm still going to do a propane enrichment test.


One thing that was concerning is the fuel pressure seemed to be a little lower than where the tuner states he thought he had set it at. I'm running a magna fuel bypass regulator. I have a twin pump setup and I swapped the primary and secondary pump circuits at idle and there was no fuel pressure change. Changed the filter, no change. Regulator even appears to be rising 1:1 with boost. It hasn't budged in pressure since the problem started, but my tuner said he set it at 58psi priming and now it's only 54 psi.

Two things I thought were odd though is 1) this isn't the first time fuel pressure was set to a given point and seemed to have possibly dropped. When I first fired the car up I was working with a remote tuner, the car ran great for a little while and then did the same thing it's doing now. I checked the fuel pressure and it was a few PSI lower than where my tuner told me to set it. At the time I just thought i was crazy and didn't set it right, but in the back of my head I kept thinking it was weird because I was pretty sure I had set it pretty carefully.

Second weird thing is with 15PSI of vacuum, the regulator is at 42PSI but when unplugging the vacuum it only rises to 52psi. IF the regulator is 1:1, shouldn't it be rising 15psi and not 10?

Anyone have any similar issue with a boost reference regulator not staying where initially set? Think i'm barking up the wrong tree with this issue? Super frustrating, finally got this car running great/idling smooth/shifting awesome after 3 years and 3 tuners so for it start having problems after a few days is driving me nuts.

 

I'm pretty sure you have 15" of vacuum, and not 15#.
Don't take that as me being a ***, but there's a big difference, and the regulator rises on positive pressure, not so much on atmosphere.
Are you sure you don't have a mis going on?